Magnetron cavity structure and method of manufacture of same



Jan. 3, 1950 G. A. ESPERSEN 2,493,661

M ETRON CAVITY STE TURE AND THO F MANUFACT OF SAME ed March 15, 1947 IN V EN TOR.

' sizons A. zyssn y AGENT Patented Jan. 3, 1950 MAGNETRON CAVITY STRUCTURE AND METHOD OF MANUFACTURE OF SAME George A. Espersen, Dobbs Ferry, N. Y., assignor to Philips Laboratories, Inc., Irvington on Hudson, N. Y.

Application March 15, 1947, Serial No. 734,903

9 Claims.

particularly to a magnetron cavity structure and the method of manufacture thereof.

Magnetron cavities which are designed for operation at ultra-high frequencies, for example in the centimeter wave band range, are difiicult to manufacture because of the exactness required in the dimensions and the small tolerances permissible if operation is to be satisfactory. One of the common methods heretofore utilized has been to press the cavity out of copper or other high conductive metal by means of a hob. The hob was exceedingly diflicult to produce and the desired exactitude was not always achieved. Furthermore, the cavities pressed out by this method were not invariably of the same size within the required limits of tolerance due to slight nonsimilarity of the metals used for the cavity structure. Moreover, for high frequency cavity structures wherein the cavities had dimensions of the order of a radius of say .2 to .4 inch, thistechnique was time consuming, and was particularly wasteful in time for the construction of experimental models or for the construction of only a few magnetron cavity structures of a given design.

It is an object of my invention to provide a new and novel magnetron cavity structure.

It is another object of my invention to provide a new and novel method of manufacturing a magnetron cavity structure.

It is a further object of my invention to provide an integral magnetron cavity structure which is composed of different metals.

It is a further object of my invention to provide a magnetron cavity structure which can handle greater amounts of power than structures of like size heretofore manufactured.

Another object of my invention is to provide a method for the manufacture of magnetron cavity structures which is more expeditious and economical than prior methods.

Other objects, advantages and novel features of the invention will become apparent as the specification progresses.

In accordance with my invention the foregoing objects are realized by forming a matrix having a contour conforming to a portion of the cavity to be formed and slotted regions in which are inserted metal vane-like portions which are to constitute another portion of the cavity to be formed. The said vanes are initially assembled in the said matrix and the so formed assembly is electro plated whereby a composite assembly of vanes and matrix is formed. The said composite assembly is "then subjected to a suitable solvent.

which preferentially dissolves the matrix, leaving intact the vanes and electrodeposit thereby to form the desired magnetron cavity structure. In a preferred arrangement, in accordance with the invention, the vanes consist of a refractory metal, and in order to facilitate the adherence of the electrodeposit to the same, I provide the refractory metal with an initial surface plating at the region where the two metals are joined, as later to be more fully described.

In order that the invention may be more clearly understood and readily carried into effect it will now be described more particularly with reference to the accompanying drawing in which:

Figure 1 is a cross-sectional view of a magnetron cavity structure of the so-called rising sun yp Fig. 2 is a cross-sectional view of sectors which illustrate the successive steps of manufacture of the structure of Fig. 1; and

.Fig. 3 illustrates schematically the electro-deposition of metal on the matrix and inserted mem- Referring now to Fig. 1, the magnetron cavitystructure 6 has radially extending vanes or members 8 of copper, and adjoining thereto at the outer ends I 0 of vanes 8, radial extensions I2 also of copper. The extensions I2, as will appear more particularly hereinafter, are formed by electro-deposition. The circumferential portions I4 complete the enclosures of the smaller cavities l5 and the outer circumferential-portions I6 complete the enclosures of the larger cavities I8. The entire cavity structure thus provides nine large electro-magnetic cavities I8, and nine smaller electro-magnetic cavities I5, each smaller cavity being located diametrically opposite a larger cavity.

Fig. 2 is a cross-sectional view of the 60 sectors A, B, C, D, and E of the structure of Fig. 1 in various stages of manufacture. The view is taken normal to the axis 22. Referring first to sector A of Fig. 2, first I take a cylindrical piece of aluminum having an outer radius after polishing which is equal to the desired internal radius of the larger cavity sections I8. In the illustrated structure this radius is .3175 inch. I prefer to use copper-free machinable aluminum which may be accurately'worked on a milling machine. I then mill nine slots 32 at regular intervals about the axis as shown in sector A of Fig. 2. Each slot 32 is milled toa .depth so that the inner face 34.

3 thereof is .1985 inch radially distant from axis 22. The side faces 36 of the slots are substantially radial. I find it desirable to cut the slot 32 somewhat scant, for reasons which will appear subsequently, and therefore the faces 36 of each slot 32 are separated very slightly less than 20.

Referringnow to sector B of Fig 2, 1 next-cut slits as time the sides is inwardly toward the axis 22, using a thin circular saw on the milling machine. These slits are .008 inch wide and ex= tend radially and axially. In cutting slits 38 I prefer the face 36 to join smotithiy 'with thle side] of the slit. Therefore, I cut awaiit'lie slight per:

tion which I have allowed to "remain on the face of the slots for that purpose; which niay amount to a matter of a thousandth of an inch or so. Slits 38 are cut to such a depth that-the distance of the terminations 39 thereof tram 'axis 2? is .0455 inch corresponding to the desired internal radius of the inner terminations of vanes 8 of Fig: 1-, {or slightly less,- for 'a reason which will appear hereinafter. This leaves nine smallwmatrix segments 40 and nine large matrix segments M which substantially correspond respectively in dimensions to the desired small cavities i5 and large cavities [8 of Fig. 1. 7

Referring now tosector .C of Fig; 2, copper inserts 1dr vancsB, preferably of oxygen-free high conductivitycopper;are made deep enough to fit the slits 38 and just wide enough to make a close sliding fit therein. After de=grea sing the matrix, I-then slide these vanest intoslits 38. prefer to form a face :12, corresponding to the outer end In of Fig- 1 on "one'of the=edges of each va'ne B-at an angle of about'45 degrees so that after inserti'on a smooth joining at substantially a 45 angle is made between smaller matrix segments and faces 36 of the l'argr'matrix sigm'ents "M, as illustrated; The appearance of thecros's' 'sec tion of the matrix now presents the larger segments 4'1 made in this instance of alumiii'um with the copper'vanes't-joini-hg the 'smallersegmentsm to the matrix body. There are nine of the slots 32' ahd'there are also ninc each cf the segments 4'0 and II. There are eighteen copper inserts or vanes 8. J

Referring new more particularly to 1 i'g-.-'3,-be-

' fore-returning again 't rig. -1 nave slicwn schematic forfli the method whereby the "asseiirbled matrix and theiiisertd vanestare e1ectro-' plated. I 'iilake a copper "s'iiliohate SOfilfiGIl or other apprc nate elieiitrfal-yte foi "iipiii plating. in which 1 place the 'iflatril'r and the inserted vaiis, whichfshbi'lld be fifst "'iieaneii to remcve grease and oxides. 'bly t' of matrix 'ai-ld vanes is indicated call-y in Fig. st-ye circle. assembly '6" is co 'cted the'cathtfde and a tubular cylinder 50 of carrier as the aniide withahy suitable power surplysz. nl's'o'in dicated m a general way is agitate-r 54 tcstir' the liquid electrolyte to encourage uniform plating. I have found that it is well "to iitiligi-ah aiiode which is atle'ast six "to eight times as larg in radius as the I cathode 6', and a low-average initial-c eats-en sity ef'thetruer of 3 'ainperes sqaare d im'eter. I have also foirh'd'thdtit is best to apply-the plating in coatings. Preferably, the first coat or two should 'no'texced about 5005 in-ch. -liftei' the met coat i's a'pplied the coated assembly should be re= moved from the electrolyte and polished. f find it convenient to polish the plated assembly "on a lathe lisin'gia fine crociis cloth on the *outer air-- culiife'ren'tial surface to smooth aiiy heaivygfanih 4 faces 34, as the copper deposits with such slowness on these latter surfaces that no heavy granular copper forms, as is likely to form on the outer circumferential surfaces where it deposits more rapidly. I have found that the angled faces 42 tend to keep a more uniform plating in the corners'and'give amore secure structural rigidity to the-finished cavity, although a square face may be used also. If desired the vanes 8 may be made dee enough to reach radially to the outermost diameter of the face 36. After plating and polishing successively and'slowly to a sufficient desired depth the cathode 6' may be removed. It may be desirable once or twice during the process to file lybd'enuin vane. to clean it and to reduce any lar deposit. No attentidn is necessarywto :tlie 1 slightly the corners 55 which may deposit too freely, because of the increased current density at the extending corners as indicated by the dotted lines, which are greatly exaggerated.

Upon removal from the final plating bath, the appearance of the matrix with its inserted vanes and plating will be as shown in the sector D of Fig. 2.. The assembled matrix and vanes then constitute a substantially integral structure of aluminum. and copper, with the copper forming the prospective cavity Walls of the proper dim'rrsion's.

At this point it isconvenient to cut the assembled matrix and cavity structure into the desired axial lengths, so that, upon dissolution of the aluminum, the final cavity structure-is fullyiprepared for assembly in the magnetron, ahd-one'of the faces I 6 may be removed to afford a junction with a wave=guide output'in the assembled magnetro'n. Also at this point it may be found d'e-' sirable to'dr-ill an axial hole in the matrix which will more accurately dimension the ends 39 the vanes by cutting them simultaneously to the desired diameter, as I have discovered that the vanes are not always completely inserted to the desired depth. The aluminum body affords a structural strength which avoids any distortion of the prospective cavity walls during'the'cutti-hg o'r drilling process, if care is'exercised, especially in cutting, since the copper is not closely bonded to the aluminum and may b'e'strip'ped therefrom if one 'iscarele'ss'." 1 use a rubber bended wheel for cutting the 'a'ssemblyinto axial lengths. The

ti ix sufficiently Ring to twelve 61 more l lengths from the plated assembly.

The Yacht step is Hislsliie the allihi'i'iiufifby a selective er preferential iiquid bath, thereby leaving a stliu tilfe-"llh aslllustrated 133 -13118 tor E of Fig. 2 or the finished-cavity structure of Fig. 1. This may be afifi-i piish ed cfiiiitl'y a bath of caustic solution, for xa inple sdiuin hyarcxlrl'e, which attacks the btit net the copper. V 7

Referring how more particularly to Fig. 4, the vane 'orinsert 8 is made of mol buenum'an'tl nas a thin "plating of copper 60 on the --tace ti". vanes ti may be usedinstead of the copper vanes 8 o 'f Figs. for 2. In order to attach: alayer of cc'p pert'o the face 42, I first hydrogen 'fire ithe-incoxide. Next'zt'he sides adjacent to face #2 are masked and'then the exposed face copperiplated.

Following the p1ating,,I remove the masking and inorder to bind securely the small copper layer I heat treat the vane in hydrogen. It is clear that a copper plating could be joinedto the face 42' to the exclusion of the adjoining sides by plating and then polishing the plating from the sides without necessarily using a masking technique. Thereafter I insert vane 8' in the slit 38, having computed the radial length thereof so that after copper plating the face 42 the copper plated surface is of substantially the same length as the vane 8. Thereafter the assembled matrix and vanes may be copper plated as before, and the matrix may be dissolved as before. The solvent may be warm, or at room temperature, but it is best not to have it at a boiling temperature. The resulting structure is the same as that of Fig. 1, except that the vanes 8 will be made of molybdenum and the remainder of the structure will be made of copper.

One advantage of such a structure resides in the fact-that the vanes 8' close to the cathode space 24, being made of molybdenum, a refractory metal, can withstand a great amount of heat without any deleterious effects, whereas the remainder of the wall portions, although of copper, are exposed on the outside of the structure to cooling effects by radiation or cooling conduction currents or both. The refractory metals tungsten or molybdenum may be used as vanes or inserts. The same process used to make the structure with molybdenum vanes may be used to make one with tungsten vanes. Although the Q of the resulting cavity structure is lowered because the electrical conductivity of the molybdenum is less than that of copper, the greater power handling capacity of the final magnetron more than compensates for the lowered Q. Moreover, a filament such as tungsten highly heated may be utilized and the heat thereof does not destroy or adversely aifect the cavity walls.

While I have described my invention with a specific example and application, other variations will suggest themselves to those skilled in the art. As an example of some of these variations it may be mentioned that the matrix may be made of aluminum and the plating and inserts of silver, or the matrix may be made of copper and the plating and inserts of gold. In the latter case a selective solvent might be nitric acid. Any suitable metal may be used for the plating, and an appropriate metal for the matrix. It will also be apparent that one might use a plastic matrix and an appropriate metal and solvent, although to the present time I have found it best to utilize an aluminum matrix with copper plating or an aluminum matrix with the composite cavity structure of molybdenum and copper, as herein described. If a plastic matrix is used, the finely granular metal initially deposited on the matrix to form a conductive surface for electrolytic plating causes a granular inner cavity surface which may be smoothed by a bath which attacks slowly the metal used. Because of these many variations which it is impractical to describe completely, I intend to include these and such other variations as may suggest themselves to those skilled in the art without departing from the scope and spirit of the invention as defined in the appended claims.

What I claim is:

l. The method of manufacturing a magnetron cavity structure comprising the steps of inserting members of a first metallic material into a matrix of a second material different from said first material, depositing a metallic material different from said second material on exposed portions of the matrix and inserted members and preferentially removing the matrix whereby acavity structure is formed with said inserted members form- -ing a portion of the walls of said cavity structure.

2. The method of manufacturing a magnetron cavity structure comprising the steps of forming a matrix of a first material, inserting in the formed matrix members of a second metallic material, plating on the exposed portions of the matrix and inserted members a metallic material different from said first material, and removing the matrix whereby a cavity structure is produced having walls formed in part by said inserted members and in part by said deposited metallic material. v I

3. The method of manufacturing a magnetron cavity structure comprising the steps of cutting a'slit in a matrix of a first material, making a vane of a second metallic material to be received by said slit, inserting said vane in said slit, depositing a metal 'upon exposed portions of said assembled vane and matrix, and preferentially dissolving said matrix whereby a magnetron cavity structure isproduced.

4. The method of manufacture of a magnetron cavity structure comprising the steps of forming a matrix of a first metallic material with slotted portions adapted to receive an insert, forming an insert of a different metallic material to be received by said slotted portions, inserting said inserts into said slotted portions, plating exposed portions of said assembled matrix and inserts with a highly conductive metal different from said matrix material, and preferentially dissolving said matrix whereby a magnetron cavity structure is produced.

5. The method of manufacturing a magnetron cavity structure having radially extending vanelike portions, comprising the steps of milling slots extending axially and radially in a cylindrical member of a first metal, cutting slits extending axially and from along the sides of said slots radially inwards, inserting metallic inserts in said slits, plating exposed portions of said member and said inserts with a metal, and preferentially dissolving the metal of said member whereby a magnetron cavity structure is produced in which said inserts form said vanes.

6. The method of manufacturing a magnetron cavity structure having vane-like portions of a refractory metallic material and the remaining cavity wall portions of a different metallic material, comprising the steps of milling slots in a cylindrical member of a metallic material different from said cavity structure materials, cutting axial slits in said member extending radially inward from along the sides of said slots, forming vane-like inserts of a refractory metal adapted to be received by said slits, inserting said inserts in said slits, electro-depositing a highly conductive metal on exposed portions of said assembled member and said inserts, and preferentially dissolving the metal of said member whereby a magnetron cavity structure having vane-like portions of a refractory metallic material and having the remaining cavity wall portions of a different metallic material is produced.

7. The method of manufacturing a magnetron cavity structure having vane-like portions, comprising the steps of milling slots in a cylindrical member of aluminum, cutting axial slits extending radially inward from along the sides of said sesam sum, raming wane-like mserts ata min ether than aluminum and adapted to be reat-wed my salid "slits, inserting said vane-likeihmts in said slits, successively -electr'o-pleitirig a hielily -60!!- dudtive metal on exposed portions *o'f said as senibied' member and said inserts and polishin'g said eletro-pl'ated "assembly, "cul'ifii'ng 'saiii plated and polished assembly into axial lengths, and preferentially *di'ssdlv'ing fihe alunilnum vi'h'teby a magnetron cavity structure having vanelike portions is produced.

'B."rhe'metho,d of manufacturing a magnetron cavity structure having vane-like po'fiifons; compzi'singthe stepso'f'millifig slots in'a, eylintli'iefil member ofaluminum, cutting airilslit's extend: ing radially inward from 510112 the sides (if said slots, forming vane-like inserts of a metal filir than Tahiminum an'd 'aidafitd "to f be 'recived by 7 said slits, irisitting said vane-like insertsin said slits, successively electro-plati ng a highly conductive metal on exposed portions dfsa' iqi 'as' sembled member and said insertsandplishing said e'lectroeplated assembly, axially drilling 'and cutting said plated and polished assembly into axial lengths, and preferentially dissolving :the aluminum whereby a magnetron-cavity structure having vane-like z-portionsis produced.

9; a magiietmneavisy szruature definiifg ramany mounted zl'temete :"small and large sectarlike cavities, said small cavities being-diamtrically op'pos'ed to said largeca'ivifiles, saiil striicture comprising "vane llke cavity Weill ortions e: a preformed metailintervening 'and'separatingsalifl small and largecawiities'and cavity wall portions 

